class LinkedListCycle {
  isCycle (head) {
    let p1 = head;
    let p2 = head;
    while (p2 != null && p2.next != null) {
      p1 = p1.next;
      p2 = p2.next.next;
      if (p1 == p2) {
        return true;
      }
    }
    return false
  }
}
class Node {
  constructor(data) {
    this.data = data;
    this.next = null
  }
}

let node1 = new Node(5);
let node2 = new Node(3);
let node3 = new Node(7);
let node4 = new Node(2);
let node5 = new Node(6);
node1.next = node2;
node2.next = node3;
node3.next = node4;
node4.next = node5;
node5.next = node2;
console.log(new LinkedListCycle().isCycle(node1));